Description :-
   1) Run the attached program.
   2) just type 1 to 30 in JTextArea . you can't see scrollbar.
   3) just type 31 . now you can see scrollbar i,e horizontal & vertical scrollbar.
   4) Press page up / page down button on the keyboard . you can see the scrollbar touch
      the uparrow & downarrow of the scroll bar.
   5) press page down key once . you can see that scrollbar is between the up arrow & down arrow. Now observe JTextArea, you can't see the last line i,e 31
   6) Once againg repeat step 4.

expected behaviour:-
   After pressing the page down arrow. the last line should not be hidden. scroll bar should touch the down arrow.

I tested this with Mustang b65 & Tiger rc b63.